Fiberglass Tanks and the Storage of Caustic Soda

caustic soda storage tanksLiquid caustic soda is corrosive. Currently caustic soda is stored in fiberglass, stainless steel, carbon steel, low-carbon steel, lined steel and plastic materials. The nature of the service environment, including the temperature and concentration, will largely determine which materials are most appropriate. Due to the dynamic nature of chemical storage and chemical processes, it is important to not search for a panacea. Instead there are many opportunities for employing a multitude of materials, where fiberglass can be an excellent choice, depending on circumstance. For example, when storing caustic soda, stress cracking and embrittlement in unlined soft steel has been know to occur when liquid temperatures exceed 45 degrees Celsius. Other considerations such as the use of compressed air during unloading will affect the choice of materials and also operating conditions with respect to those materials.

Storage materials are just one facet of the much larger framework, which once must consider with respect to design elements. Other considerations may likely include, but are not limited to, cavitation, solidification, pressure, vacuum, filling lines, vent lines, overflow lines, tank fluid measurements, tank foundations, tank supports and secondary containment structures when specified by relevant laws and regulations.

The purpose of this article is to identify fiberglass as a key caustic soda storage material, identify benefits of using fiberglass for the storage of corrosive materials and to outline Beetle’s custom tank offerings. A key takeaway from this article is evident when endusers, leverage the inherent strengths of fiberglass, specifically long life cycles, whereby degrees of cost-effectiveness may be realized. Another key takeaway relates to the enhancement of complex design through integration; the constructability of our fiberglass materials imparts the ability to interface to pre-existing design elements or infrastructure; this point also emphasizes design flexibility as a key characteristic of fiberglass in general.

The edict that fiberglass is an excellent corrosive storage material, with many benefits passed on to end-users, is not new. Many scholars and industry professionals alike have cogently argued that fiberglass is a superior construction material when one considers the entirety of its benefits portfolio. The key benefits of fiberglass pertinent to this topic include: light-weight, high strength-to-weight ratio, corrosion resistance via customizable corrosion barriers or liners, ease of repair, non-reactive, reduced-maintenance costs, durability, constructability and cost-effectiveness.

Beetle offers single-source design build capabilities combined with over 50 years of fiberglass experience; our products are venerated by a multitude of industries because we understand how to execute and deliver custom fiberglass products. Our tanks and vessels are employed in broad range of applications; we offer horizontal tanks, vertical tanks, chemical storage tanks, chemical vessels, as well as, transport tankers. We offer standard diameters up to 14 feet, with custom diameters available, standard materials or custom formulations.

When designing corrosion resistant fiberglass materials for caustic soda, hydrochloric acid, sulfuric acid, or any other corrosive substance the corrosion barrier will be critical. The corrosion barrier is typically fabricated with a resin-rich liner or corrosion barrier, followed by a glass-rich structural wall. The corrosion barrier is one component of the entire laminates schedule; it is a critical layer that must be designed properly in order to ensure effectiveness, safety and performance of your fiberglass product. We hope that this article has provided you with some basic details regarding fiberglass as an effective material of construction for caustic soda and other corrosives.

Corrosive Chemical Storage Problem Solved Using Fiberglass Tanks

When the team at a chemical processing plant needed a new solution for corrosive chemical storage they reached out to a number of tank suppliers and asked them to solve a few core problems.  The existing rubbr lined HDPE tanks were being used to protect against the corrosive nature of the material being stored but were not meeting the needs of the customer.  The rubber liner erodes after a few years and required re-lining causing significant downtime and added costs.

corrosive chemical storage tankThe HDPE leached acid and could not meet the pressure and vacuum requirements. The solution needed to safely store chemicals with very low pH for an extended period at a high temperature.

The tanks needed to be built for an ambient temperature range of 20 to 115 degrees Fahrenheit, allow agitation, and not require an internal coating that needed to be repaired or replaced.

“We chose Beetle based on their experience and expertise with this type of corrosive material storage tank.  The fiberglass solution they provided was the best investment in terms of cost and avoiding downtime.  The fiberglass chemical storage tanks from Beetle were delivered on time or even early and the installation and after sales service has been excellent.”

The tanks Beetle supplied were 12’ diameter by approximately 16’ tall and were designed to integrate into the customer’s processes.  One tank was a flat bottom and the other design a conical bottom both of which were custom made to fit the customer’s specific process needs.

Beetle Plastics, founded in the 1950’s, designs and manufactures custom fiberglass pipe, large diameter fiberglass ductwork, fiberglass tanks, fiberglass vessels, other equipment and services relating to fiberglass products. 

Beetle Plastics is a subsidiary of Midwest Towers, Inc., a world-class manufacturer of evaporative water cooling towers. Beetle Plastics operations include our headquarters and plant facilities in Ardmore, Oklahoma, and a nationwide network of sales and representative offices.

The Storage of Sulfuric Acid in FRP Composite Tanks

Sulfuric acid (H2SO4) is a chemical that presents unique handling and storage problems. In the higher concentration ranges (96% to 97%), sulfuric acid (66Be’) can be stored in cast iron or carbon steel.  High concentrations of sulphuric acid, however, are very detrimental to FRP composite equipment. At these higher concentrations, sulfuric acid must not come in contact with FRP laminates.

Diluted sulfuric acid, on the other hand, is very aggressive toward cast iron or steel tanks, but can be stored and handled very well in FRP composite equipment. FRP composite equipment is best suited for concentrations of 70% sulfuric acid and below. At 75% sulfuric acid, the maximum temperature allowed with vinyl ester resins is 100° to 120°F. As the concentration decreases, the allowable temperature limits increase.

The procedure for dilution of concentrated sulphuric acid that has worked best in fiberglass composite vessels is as follows:

1. First, add to the storage vessel the entire amount of water required to achieve the desired solution concentration.

2. Then add the concentrated acid slowly into the center of tank by using one of the following suggested fittings:
a) an FRP top nozzle with a PVC flanged down pipe.
b) a PVC coupling and down pipe.
c) a 316 stainless steel coupling with a 316 stainless steel down pipe. The reason the concentrated sulfuric acid is added to the tank center is to prevent concentrated acid from coming in contact with an FRP composite nozzle, or sidewalls of the tank. The concentrated acid should not be allowed to drop onto the liquid surface. Introduce the concentrated sulfuric acid 2” to 3” below the liquid surface. One method of accomplishing this is to create vortex by adding baffles from the bottom of the tank to the height that concentrated acid is first added to the tank. Another alternate method is to extend the down pipe 6” below
the liquid surface.

3. During the dilution process, the mixture must be continually agitated to insure adequate dilution and prevent high concentrations of sulfuric acid from settling and damaging the FRP composite tank. To insure adequate dilution, a rubber-coated agitator, or pumping the tank continuously through a side bottom drain,is required. Circulation through any nozzle on the tank bottom could result in heavy viscous concentrated acid settling to the tank bottom and destroying the FRP composite tank below the nozzle.

4. The dilution of sulfuric acid generates considerable amounts of heat. The temperature of the diluted sulfuric acid must be controlled below 150°F for finished concentrations of 50% or less, and 140°F for 50-70% sulfuric acid solutions. This can be accomplished by regulating the flow rate of concentrated sulfuric acid addition, or by external cooling of the tank contents.

5. The preferred type of FRP composite vessel for storing sulfuric acid is a non-insulated, vertical, above ground tank. Even underground tanks, with the ground acting as an insulator, may have excessive storage temperatures.

6. Sulfuric acid (H2SO4) with trace organic impurities can cause reduced service life of FRP composite laminates.

Contact us today about your fiberglass pipe and fiberglass tank requirements.